The present invention relates generally to synchronization of clocks and, more particularly, to synchronization of clocks in a packet-switched communication network.
It may be advantageous in a networked system for devices in the network to have a common time base. The common time base may be used, for example, to trigger coordinated measurement instances in a network of sensors or to coordinate actions of controllers in an industrial system. In addition to sensors and controllers, the system may include computers and communication devices, such as routers.
The communications industry has developed several standards for use in synchronizing clocks, for example, the Network Time Protocol (NTP), ITU-T Y.1731, and the Precision Time Protocol (PTP) of IEEE 1588. PTP includes sending timing-related synchronization messages between nodes in a communication network. The synchronization messages include, for example, a node transmitting a time-stamped packet to supply its timebase to another node and a node transmitting a packet requesting the receiving node to reply with the time of receipt in order to measure the delay between the nodes. Any errors in handling the synchronization messages may be detrimental to accurate clock synchronization and the harm may be cumulative over multiple network devices. Furthermore, some portions of a communication network may not be equipped to handle synchronization messages.